In recent years, environment-friendly vehicles, such as electric vehicles, fuel cell vehicles and hybrid vehicles employing both a motor and an engine, have received attention. It has been considered to mount a plurality of batteries on these vehicles where power supply devices are mounted.
Japanese Patent Laying-Open No. 2003-209969 discloses a power control system for an electric traction motor in a vehicle including: at least one inverter for providing conditioned electric power to the electric traction motor; a plurality of power stages for providing direct current (DC) power to the inverter, each stage having a battery and a boost/buck DC-DC converter and the power stages being wired in parallel; and a controller for controlling the plurality of power stages so that the batteries of the plurality of power stages are equally charged and discharged and the plurality of power stages maintain an output voltage to the inverter.
It is considered to mount a plurality of batteries of multiple kinds on a hybrid vehicle in order to maintain a maximum output and increase a distance traveled when the vehicle runs by using only electric power from the batteries. In this case, it is also contemplated to use a plurality of voltage converters.
Usually, however, current sensors should be installed for the plurality of converters respectively for independent current control over the converters. It is not preferable, however, to increase the number of the current sensors because the current sensors themselves are costly and maintaining reliability thereof also requires labor and cost.